Generate sphinx source files in separate environments

Current we have this

python -m pip install -r requirements.txt

echo "Discover ewoks task libraries on PyPi ..."
python scripts/requirements.py

echo "Install ewoks task libraries for task discovery ..."
python -m pip install -r scripts/packages/requirements.txt

echo "Generate sphinx source files ..."
python scripts/generate.py

The proposal is to generate several requirements.txt files (one for each ewoks app) and generate the RST files in different environments.